Audit trail

A sequence of documents in which every link names the one before it. A statement line carries an amount and a date; the trade confirmation behind it carries the instrument, the direction, the size, the price and the timestamp; the platform's own order history carries the instruction as it was sent, including the levels attached to it and any later amendment. Read together they answer where a number came from. Read separately none of them does, which is why the chain rather than any single record is the object.

The property that makes it useful is that it is contemporaneous. Each link was written at the moment the event happened, by a party with no knowledge of how the position would end, which is exactly what a recollection formed afterwards cannot offer. A firm operating under an authorisation is required to keep records of this kind for a stated minimum period and to produce them on request, so the chain is an obligation on the firm rather than a courtesy, and a gap in it is a question the firm has to answer.

What it settles and what it does not are worth holding apart. It settles what was instructed, when, at what price and for what size, and it settles whether a charge was applied on the basis the terms describe. It does not establish that a decision was sound, and it does not turn a disputed judgement into a factual matter. A complaint that rests on the trail tends to be resolvable; a complaint that rests on what a reader believes was implied usually is not.